Electro Au Bump

Au bumping & COG (Chip on Glass) bonding technology is currently used for mounting the LDI (LCD Driver IC) by some companies. Currently, Au bump is formed by electroplating with KAu(CN)2 which is hazardous. Also, it is very difficult to make a fine PR(Photoresist) pattern due to the chemical attack of cyanide compounds. To solve this problem, the non-cyanide gold solution was developed and applied for mass production. Microscale adopts the electro-plating method using the non-cyanide gold solution?and an effort for stabling the best process conditions for mass production is being made to control the bump to bump pitch of 10 um. On the other hand, the electo-plating technique to obtain uniform thickness profile for 6" wafer was already established, but the technique for 8" wafer was developed by only a few companies. Microscale has developed the Au electroplating processes and will apply these processes for Au bump mass production to control the thickness of 18 um +- 5%.

Another issue in Au bump process is its mechanical strength. The hardness of Au bump is one of the most important factors that determine the yield in COG process. Currently required hardness of Au bump for applying the COG process is higher than 50Hv. In the case of the Au bump formed using non-cyanide compound, the hardness of Au bump can be adjusted by thermal annealing. Microscale will manage the strength of Au bump in the range of ~60Hv.

UBM(Under Bump Metallurgy) offers good adhesion between the bump and the pad in forming the Au bump. The reliability of bump depends on what kinds of UBM are used. Microscale will?use TiW as a UBM which shows good reliability. Microscale also is developing the new UBM structure that is more stable and reliable than TiW and it will be applied as soon as possible in mass production.

ACF is widely used in order to mount the Au bump LDI chip on the LCD panel. Various ACF have been developed and are solded. The characteristics of interconnection using ACF depend on the concentration of the filler particles and components of the filler. Microscale already developed ACF that shows better electrical and mechanical performance in cooperation with KAIST. In high humidity test condition of 85C/85% RH, the electrical contact resistance of the flip chip interconnected using the ACF did not changed for 1000 hours.Temperature cycling test (-50C to 165C) shows that newly developed ACF can endure for 700 cycles. Microscale will adopt this ACF in mass production process.

Bump Height : 18 um

Bump size : 89 um

Pitch : 100 um

Material : Au

UBM : TiW